Free CPO Tonometry Principles and Procedures Questions and Answers 1 — Questions and Answers
Question 1: What is considered the 'gold standard' for measuring intraocular pressure (IOP)?
- Non-contact tonometry (NCT)
- Goldmann applanation tonometry (GAT) (Correct answer)
- Schiøtz tonometry
- Digital palpation
Correct answer: Goldmann applanation tonometry (GAT)
Goldmann applanation tonometry (GAT) is widely regarded as the most accurate and reliable method for measuring IOP. It serves as the benchmark against which other tonometers are compared. The procedure involves using a special prism at the slit lamp to flatten a small area of the cornea.
Question 2: The Goldmann tonometer measures IOP based on the Imbert-Fick principle, which relates pressure to the ______ required to flatten a specific area of a sphere.
- Volume
- Time
- Force (Correct answer)
- Temperature
Correct answer: Force
The Imbert-Fick law states that for an ideal, dry, thin-walled sphere, the pressure inside is equal to the force applied to flatten its surface divided by the area of flattening. The Goldmann tonometer is designed to apply this principle to the cornea by measuring the force needed to flatten a 3.06mm diameter area.
Question 3: Which of the following factors can cause a falsely LOW IOP reading with Goldmann tonometry?
- A thick central cornea
- A thin central cornea (Correct answer)
- Patient squeezing their eyelids
- Poor calibration of the tonometer
Correct answer: A thin central cornea
Corneal thickness affects the accuracy of GAT. A cornea that is thinner than average provides less resistance to flattening, resulting in an artificially low IOP reading. Conversely, a thick cornea can lead to a falsely high reading.
Question 4: When taking a measurement with a Goldmann tonometer, the correct endpoint is reached when the inner edges of the two fluorescent semi-circles (mires) are:
- Widely separated
- Overlapping significantly
- Just touching (Correct answer)
- Fused into a single solid circle
Correct answer: Just touching
The operator adjusts the force dial until the inner margins of the green semi-circles, viewed through the prism, are just touching. If they overlap, the pressure reading will be too high; if they are separated, the reading will be too low. This alignment indicates the correct area of the cornea has been flattened.
Question 5: How does a non-contact tonometer (NCT), or 'air-puff' tonometer, measure intraocular pressure?
- By measuring the electrical resistance of the cornea
- By analyzing the reflection of sound waves
- By measuring the corneal response to a puff of air (Correct answer)
- By gently indenting the cornea with a weighted plunger
Correct answer: By measuring the corneal response to a puff of air
The NCT emits a controlled puff of air towards the cornea. An optical sensor measures the time it takes for the air to flatten a small, specific area of the corneal surface; a higher pressure inside the eye requires a stronger puff (or shorter time at a set force) to achieve flattening.
Question 6: What is a critical step that must be performed before using a Goldmann tonometer tip on a patient?
- Calibrating the tonometer at the '2' mark
- Rinsing the tip with tap water
- Disinfecting the tip according to office protocol (Correct answer)
- Warming the tip to body temperature
Correct answer: Disinfecting the tip according to office protocol
The tonometer tip directly contacts the patient's anesthetized cornea, creating a risk of transmitting infectious diseases. Proper disinfection with an approved agent (like an alcohol wipe or dilute bleach solution, followed by rinsing and drying) is essential for patient safety.
Free CPO Tonometry Principles and Procedures Questions and Answers 1
What is considered the 'gold standard' for measuring intraocular pressure (IOP)?